<template>
    <div>
        <router-link 
            tag="div" 
            to="/" 
            class="header-abs"
            v-show="showAbs"
        >
            <div class="iconfont header-abs-back">&#xe624;</div>
        </router-link>
        <div class="header-fixed"
            v-show="!showAbs"
            :style="opacityStyle"
            >
            <router-link to="/">
                <div class="iconfont header-fixed-back">&#xe624;</div>
            </router-link>
            景点详情
        </div>
    </div>
</template>
<script>
export default {
    name:'DetailHeader',
    data (){
        return{
            showAbs:true,
            opacityStyle:{
                opacity:0
            }
        }
    },
    methods:{
        handleScroll (){
            const top = document.documentElement.scrollTop
            if( top > 60 ){
                let opacity = top/140
                opacity = opacity >1 ? 1:opacity
                this.opacityStyle = { opacity }
                this.showAbs=false
            }else{
                this.showAbs=true
            }
        }
    },
    activated(){
        //全局事件  如果不解绑 会影响其他的组件
        window.addEventListener('scroll', this.handleScroll);
    },
    deactivated(){
        //页面即将被隐藏的时候会执行这个方法
        window.removeEventListener('scroll', this.handleScroll);
    }
}
</script>
<style lang="stylus" scoped>
    @import "~styles/varibales.styl"; 
    .header-abs
        position :absolute
        left:.2rem
        top:.2rem
        width :.8rem
        height :.8rem
        border-radius :.4rem
        line-height :.8rem
        text-align :center
        background :rgba(0, 0, 0, 0.8)
        .header-abs-back
            color :#fff
            font-size :.4rem
    .header-fixed
        z-index: 2
        position:fixed
        top:0
        left :0
        right :0
        height :$headerHeight
        line-height :$headerHeight
        text-align :center
        color :#fff
        background :$bgColor
        font-size :.32rem
        .header-fixed-back
            position:absolute
            top:0
            left :0
            width :.64rem
            text-align :center
            font-size:.4rem
            color :#fff
</style>